18
J. Org. Chem. 1993,58, 18-20
A Highly Catalytic and Selective Conversion of Carboxylic Acids to 1-Alkenes of One Less Carbon Atom Joseph A. Miller,*J Jeffrey A. Nelson, and Michael P. Byrne Henkel Research Corporation, 2330 Circadian W a y , Santa Rosa, California 95407-5415 Received October 20,1992
Summary: An equimolarmixture of a carboxylicacid and acetic anhydride produces a reagent combination that undergoesa highly efficientdecarbonylationtdehydration at 250 OC using either Pd- or Rh-based catalyst systems, affording excellent yields of the corresponding 1-alkenes of one less carbon atom. The stoichiometric and catalytic decarbonylation of aliphatic aldehydes and acid chlorides to alkanes and alkenes, respectively, by transition-metal complexes are well-known and synthetically useful Relatively little, however, has been reported concerning the analogous decarbonylationtdehydration of aliphatic carboxylic acids to olefins, with generally poor results achieved in terms of catalyst efficiency and selectivity toward terminal olefin formation in the p r o d ~ c t .For ~ example,the decarbonylationtdehydrationof stearic acid to heptadecene using a Rh-based catalyst was reported to proceed with a masimum catalyst turnover number (TON moles of olefin product formed per mole of catalyst used) of ca. 250, with selectivities toward 1-heptadecene formation typically below 50%.3c Interestingly, results were presented in this work which suggested that the decarbonylation of stearic acid proceeded via intermediate formation of stearic anh~dride.~ Use of a preformed, symmetrical anhydride is not desirable from an economic or synthetic viewpoint, particularly since its decarbonylation should result in the formation of equal amounts of olefin and carboxylicacid coproducts. We now report here that the use of a carboxylicacid substrate as an equimolar mixture with acetic anhydride (AczO) produces a 'mixed anhydride system"6 which undergoes an extremely facile decarbonylation reaction to provide a general and highly selective route to the corresponding 1-alkenesof one less carbon atom (eq 1).
RCH2CH2C02H+ Ac,O
Pd or Rh catalyst
* RCH=CH2
260 o c
+
CO + 2AcOH (1)
The followingprocedure for the conversion of decanoic acid into 1-nonene is representative. An equimolar mixture of decanoic acid and Ac20, together with (Ph3P)2PdC12 (1,O.Ol mol % based on the initial charge of decanoic acid) and Ph3p (50 equiv relative to the Pd catalyst), was heated in an oil bath maintained at 250 OC under a moderate flow of N2 in a round-bottomed flask fitted with a distillation head, and the distillate product formed was collected. The initial level of the reactor contents was maintained throughout the course of the entire reaction by continuously introducing a feed mixture composedof equimolaramounts of decanoicacid and AczO. Decarbonylation initiated when the reaction temperature reached 18&190 OC, as evidenced by the rapid evolution of CO6fromthe reaction vessel. Distillation of the product subsided after about 45 min of reaction time. Analysis of the distillate by GC showed the presence of 1-nonene, formed with a selectivity of 97.3%' and a catalyst TON of 12 370. No nonane was produced in the reaction, and, other than recovered decanoic acid or related anhydrides, the only byproducts detected in the distillate product or remaining reaction mixture were trace amounts (10.5% combined yield relative to nonene product) of 2-undecanone and 10-nonadecanone. Thus, taking the minor amount of recovered starting material into consideration, the yield of 1-nonene product derived from this transformation is excellent. Significantly,this reaction has been carried out on a continuous basis with the catalyst and excess phosphine dissolved in the carboxylic acidtAcz0 feed, thereby facilitatingthe rapid productionof relatively large quantities of a-olefin product.8 As demonstrated by the data in Table I, the combination of carboxylicacid and Ac2O results in substantially higher catalyst efficiency and terminal olefin product selectivity for both Pd- and Rh-catalyzed decarbonylation systems than that found by use of either the corresponding carboxylicacid aloneor preformed symmetricalanhydride. For comparativepurposes,analogousexperimentsutilizing the corresponding acid chloride and aldehyde were also carried out. It should be emphasized that heating an equimolar mixture of decanoic acid and AczO without any
(1)Present addreea: Exxon Chemical Company, Basic Chemicals Technology, P.O. Box 4900, Baytown, TX 77522-4900. (2) (a) Tsuji, J. In Organic Syntheses uia Metal Carbonyls; Wender, I., Pino, P., Eds.; Wiley-Interscience: New York, 1977; Vol. 11, pp 595654. (b) Doughty, D. H.; Pignolet, L. H. J. Am. Chem. SOC.1978,100, 7083. (c) Doughty, D. H.; Pignolet, L. H. In Homogeneous Catalysis With Metal Phosphine Complexes; Pignolet, L. H., Ed.; Plenum Press: NewYork, 1983;pp343-376andreferencs contained therein. (d)Belani, R. M.; James, B. R.; Dolphin, D.; Rettig, S. J. Can. J. Chem. 1988,66, 2072. ( e )Andrews, M. A.; Gould, G. L.;Klaeren, S. A. J.Org. Chem. 1989, 54,5257. (0Abu-Hamnayn, F.; Goldman, M.E.; Goldman, A. S . J. Am. Chem. SOC.1992, 114, 2520. (g) OConnor, J. M.; Ma, J. J. Org. Chem. 1992, 67, 5075. (3) (a) Prince, R. H.; Raspin, K. A. J. Chem. SOC., Chem. Commun. 1966,156. (b) Fenton, D. M. U.S. Patent 3,630,198,1970. (c) Foglia, T. (6) The presence of CO in the effluent gas was confirmed by FT-IR A.; Barr, P. A. J. Am. Oil Chem. SOC. 1976,53,737. analysis. (4) The oxidative addition of anhydrides to Rh(1)-phosphine com(7) The remainder of the Ce-product mixture consisted of tram- and plexes, includingthe isolationand characterization of the resultant Rh(II1) cis-2-nonene in a relative ratio of ca. 31. acyl derivatives, has recently been reported Miller, J. A.; Nelson, J. A. (8)At the conclueion of the reaction, the spent Pd catalyst is present Organometallics 1991, 10, 2958. (5) The exact composition of the carboxyUc acid/AczO mixture clearly as an easily recoverable black powder. Due to the low concentration of Pd catalyst preferably employed in these carboxylicacid decarbonylation/ depends upon many factors, including temperature and volatilization of lower boiling componenta from the solution. For inetance, an equimolar dehydration reactions, carrying out the transformation in a continuous solution of decanoic acid/Ac20 was determined by IH-NMR analyeis to fashion also provides for the generation of larger and more conveniently contain an 87:13:0 molar composition of n - C o H l ~ C O ~ H - n - C ~ H ~ ~ C O z Arecovered ~ quantities of Pd. Thie recovered Pd has, in fact, been reconverted into 1 0 and utilized in subsequent runs. (n-C&oCO)~O after 30minat 30 OC. Upon heatingat 250 OC and allowng volatile materials to distill away, the ratio changed to 1422:64 after ca. (9) Heck, R. F. Palladium Reagents in Organic Syntheses;Academic 1 min and 9982 after 30 min. Press: London, 1985.
Q 1993 American Chemical Society
J. Org. Chem., Vol. 58, No.1, 1993 19
Communications
Table I. Comparison of Various Functional Croups and Substrates in Their Pd- or Rh-Catalyzed Decarbonylation/ Dehydration to Terminal Olefins. Pd catalyst* Rh catalystc Substrate C,-1 olefii a-selectivity (%) TON TON/h C,-1 olefin a-selectivity (%) TON TON/h n-C11H&2OCl n-C11H&HO n-CgHlsCOzH n-C11H&OZH (n-CsH1eCO)20 (~-C~iHzsCO)zo ~-CeHi&OzH/AczO ~-C~~H&O~HIAC~O
76.0 d
100 40
50 20
27.7 d 97.9 78.6 97.1 86.7 97.2 96.9
e e
91.6 83.7 97.3 94.3
4310 1260 12370 7360
26000 7500 16500 17600
1,330 240 190 60 430 280 710 700
400 76 11 6 24 27 110 130
0 W reactions were carried out a t 250 O C (oil bath temperature) under a slight flow of N2, in a manner similar to that described in the text. Catalyst concentrations indicated below are relative to the initial amount of substrate present. Analyses were carried out by GC using n-decane as an internal standard. Pd catalyst: (PbP)zPdClz (0.01 mol '5%) and added Phsp (0.50 mol % ). Rh catalyst: (Me2PhP)pRh(CO)Cl(l.O mol % ). d The product consisted of a 2 9 5 5 ratio of undecane-1-undecene. e Little or no detectable reaction (TON < 6).
*
catalyst present at 250 "C for 8 h'produced
